Communication system for ultrashort radio waves



Feb. 2l, 1950 H. o. PETERSON ET A1. 2,497,958

COMMUNICATION SYSTEM FOR ULTRA sHoRT'RADIo WAVES Filed May 21, 1942 4 Sheets-Sheet 1 M/cPoP/fowf 72 KEW/vs RLTEPAMTELY Ow P191 ou@ P02 /PEcE/VE@ ow/Dess y F/Tsk GLP/1 INVENToRs i Pa. /@PoLa O. PETE/320,14, /EP F/Lre@ BY BEPYPAMPEVOR 1 "M MW PHO/"w ATTORNEY Feb. 21, 1950 H. O. PETERSON ET AL Filed May 21, 1942 COMMUNICATION SYSTEM FOR ULTRA SHORT RADIO WAVES 4 Sheets-Sheet 2 Feb 21, 1950 H. o. PETERSON ET A1. 2,497,958

COMMUNICATION SYSTEM FOR ULTRA SHORT RADIO WAVES Filed May 21, 1942 4 sheeis-sheet s Foe @WTE/ww: fis/61nlf2 eZM/Lfas' es 720 I Wf I/ I7/ L"73o i? V W /4 f loon/ER AMEL/mm 11, f, 3

Masrf 57 L-L '62 Msn-R Osc/LLAToR\ M0] M02 Osc/LATQR /Df/sf E MaauLAro/Q 76C/`r X L'. 7'7@ (ILSE /270 Osc/LLA TOR E s z ll. INVENTOR@ /MQOLD O. PETERSON, 20 BERT/aww 7951/019 C y BY ATTORNEY Feb. 21, 1950 H. O. PETERSON ET AL Filed May 21, 1942 COMMUNICATION SYSTEM FOR ULTRA SHORT RADIO WAVES 4 Sheets-Sheet 4 INVENTORS #HPO/.0 O. PETEPQSo/V,

ATTORNEY Patented Feb. 21, 1950 UNITED STATES PATENT OFFICE COMMUNICATION SYSTEM FOR ULTRASHORT RADIO WAVES Application May 21, 1942, Serial No. 443,932

8 Claims.

Our present invention relates to communication or signaling on ultra high frequency radio waves.

When signaling with fultra high frequency radio waves having, for example, a wave length of the order of ten centimeters or a frequency of the order of 3000 megacycles, it will be found that physical obstructions cast rather sharp shadows. These may be avoided by mounting the signaling antennas well above such obstacles. However, since it may not be possible, desirable or practicable to locate a single omni-directional antenna above all nearfby obstructions which cast such shadows, it is an object of our [present invention to vovercome this diilculty and to provide an omni-directional communication system for ultra short waves employing directive antennas, which system does not require unduly high supporting structures.

For example, suppose it is desired to locate an ultra short wave antenna half way up a large cylindrical tower which would cut off most of the radiation in a direction in back of the antenna; the system may be made non-directive by using two directive antennas opposite each other on the tower. Each antenna would be so designed to cover uniformly, in a horizontal plane, a little more than 180 degrees. Such an antenna arrangement having 'a uniform characteristic over a range somewhat greater than 180 degrees is described in detail in the copending U. S. application of J. B. Atwood, Serial No. 441,659, filed May 4, 1942, now Patent No. 2,401,601, granted June 4, 1946.

However, if both of these antennas were fed simultaneously there would be many dead spots in the radiation pattern because of cancellation of the radiated waves and elds in certain directions in space. To overcome such dead spots is a further object of our present invention and this object is fulfilled by providing a system in which the two antennas are fed alternately at a rate substantially albove the highest audio or, more generally, above the highest modulation frequency to be transmitted. By such an arrangement, a uniform field distribution in all directions is secured without dead spots from shadows or the cancellation points from two simultaneous transmissions on the same frequency. Incidentally, it is to be noted that the invention is not necessarily limited to transmission, but -may be used equally well for reception.

In modifications of our invention which are described herein several important advantageous features may be employed such as, for example, the use of a lpulse frequency oscillator to control the switching of power from one antenna to another and to simultaneously control the frequency of the pulses of variable length fed to the antennas; and the use `of antennas of diierent heights as well as the use `of different operating frequencies to overcome zones of low signal intensity or so-called dead spots. These Various features are used singly or in combination as will be described more fully later.

Other objects, features and advantages of our invention Vwill lbe apparent as the more detailed description thereof proceeds. This description will be given in connection with the accompanying drawing wherein:

Figure 1 illustrates an arrangement for alternately exciting two antennas, each having a uniforum radiation characteristic over something more than degrees, with modulated ultra short waves;

Figure 1A is a schematic diagram of a receiving syste-m which may be used for receiving transmissions from Figure 1;

Figure 2 is a modification of the transmitting system of Figure 1 and is characterized by the use of pulse modulation and further by the fact that the pulse modulator controls the alternate excitation of the antennas;

Figure 2A is a graph explanatory of the action of Figure 2;

Figure 2B is a modication of Figure 2 wherein transmissions occur alternately on different carrier frequencies;

Figure 2C is another modification of Figure 1 wherein the same signal is oppositely radiated from oppositely directed antenna systems simultaneously on carriers of different wave lengths;

Figure 3 is a graph illustrating variations in zones of low intensity along the earths surface for antennas of varying heights or for antennas operating on different wave lengths;

Figure 4 illustrates a transmitting arrangement for alternately exciting antennas of diiferent heights so as to avoid the dead spots of Figure 3. It is to be noted in Figure 4 that the antennas may be excited with carrier energy of the same or different frequencies; and

Figure 5 illustrates a modication of Figure 4 wherein pulses are radiated alternately from antennas at two different heights and in two directions. In connection with Figure 5 it is to be noted that all antennas may be operated on the same carrier frequency, or each pair of antennas may be operated at a different carrier frequency or, if desired, all of the antennas illustrated may each be operated on one of four different carrier Ifrequencies.

Referring to the transmitting system of Figure 1, a single master oscillator MO generating a suitable carrier frequency, for example, 3000 megacycles, is fed to Va pair of power amplifiers PAI and PA2. The outputs of the Vpower amplifiers are fed through transmission llines 2, II to a pair of directive antennas 6,,8..mounted upon a tower or other suitable support I0. The waves appearing in the output circuits of the power ainpliers, namely, in the transmission lines 2,--l, are modulated by the modulating waves here indicated to be audio frequency waves, developed by microphone M, fedto the modulator I2. The

' modulator I2, as' illustrated, is suitably coupled to the. power amplifiers so as to modulate the outputsthereof in any desired manneras, for example, to produce phase, frequency or pulse modulated outputs which are to be fed to the antennas '6, 8 through transmission lines 2, Il.

,Thepower amplifiers PAI and PAZ are also ,diierentially keyed on and off at a rate higher than the highest modulating frequency. For example, if the highest modulating frequency is from 3000 to 5000 cycles, the power amplifiers PAI and PAZ are alternately 'turned on and olf by the differential modulator I4 at aten kilocycle Aany desired amountof directivity inthe vertical plane; Preferably, antenna systems 8, 8 are 'builtfalongf the lines of Figures 3 and 4 of the copending application of J. B. Atwood, :Serial No. 441,659,.filed May. 4, 1942. By the use of such antenna systems for 6 'and 8, non-directional or omni-directional transmission and reception are achieved with directive relatively high gain antennas.

Figure 1A' diagrammatically illustrates a receiving system employing the principles of our invention. In'Figure 1A two antennas 6A and 8A, similar to antennas 0 and 8 of Figure 1, are used to feedthrough suitable transmission lines 2A Vand 4A separate receivers IR and 2R. A diode 'd'ete'ct'or DI is provided for receiver IR and a separate diode detector D2 is provided for rel ceiver'ZR. .The diode detectors DI and D2 are Aprovided with separate low pass filters FI and F2 both of which-work into a common load resistor CLR from which audio or modulation frequency .waves are. obtained to feed a low pass filter and audio amplier LPFA.A The filter LPFA is designed so as to cutoff all frequencies above the highest modulation frequency transmitted which,

in the event the highest transmitted frequency is 50.003cycles, would be 5000 cycles. As a consequence, the. differential modulator frequency of, forzexample, 10,000 cyclesffgenerated at I4'in Figmodulation.

' delivering power at a given time.

ure l is prevented from passing into the translating device, here shown as earphones EP.

The low pass filters FI and F2 associated with each of the diodes DI, D2 of Figure 1A suppress frequencies of the received carriei frequency or of the final intermediate frequency and higher frequencies used in the receivers IR and 2R.

It is to be noted that the receiving arrangement of Figure 1A allows reception from all directions despite presence of the large cylindrical tower A or other supporting structure which may extend substantially above the antennas 5A and 8B.

Also as rillustrated in Figure' 1A, the common load resistor CLR feeds through a suitable time constant circuit TC, an automatic gain control tube AGC'I in turn supplying automatic gain control voltages through connections VC. Further, it is to be noted that while the upper modulating frequency has been indicated to be 5000 cycles and the differential modulator frequency to be 10,000 cycles, other values may be used. For example, the highest modulating frequency transmitted may be 15,000 cycles for high quality voice transmission and in that event the differential modulator I4 of Figure 1 should be operated at a higher frequency, for example, 50,000l cycles.

Figure 2 illustrates an arrangement similar to Figure 1, but Figure 2 is characterized by the employment of pulse modulation and further by the fact that the pulse `oscillator is used to control switching from one antenna to another. In the type of pulse modulation used in Figure 2 the length of the pulses is varied in accordance with the percentV of modulation. This type of modulation-is sometimes referred to as constant frequency variable dot modulation. One hundred percent modulation in this case corresponds to a maximum pulse'length of fty percent mark and this approaches zero percent at zero percent In the arrangement of Figure 2 the `width of'pulses varies from zero to fifty percent for each of the power amplifiers PAI and PAZ, and since the ampliersare keyed on and off differentially or alternately only one will be The adjustmentsmay bemade such that in the case of zero audio or no modulation, each transmitter or power amplifier is being 'keyed with twenty-five percent pulses'and in the case of one hundred percent modulation with fifty percentpulses.

' Specically referring to Figure 2, the pulse oscillator vP06 feedswaves of pulse frequency, for example, sixteen kilocycles through transformer T8 to the pulse modulators PMID and PMI2.

These pulse modulators are of the constant free LZ2 to the power amplifiers PAI and PAZ and,

secondly, the oscillator P06 alternately turns on andoff the power amplifiers PAI and PAZ through'the action, of course, of the pulse modulators'PMI andPMIZ. The pulse modulators PMICI and PMI2 only vary the length -of the `pulses fed to the power amplifiers and not the rate of the pulses which, as before stated, is controlled bythe lpulse oscillatorPO.

The 'relative timing-*of the excitation of the power ampliers PAI and PAZ of Figure 2 andthe range of pulse length for maximum modulation is diagrammatically illustrated in Figure 2A. -It is to be noticed that the pulses increase and decrease in length, according to the modulation, simultaneously in the outputs of each of the power amplifiers PAI and PAZ and that both power ampliers never feed energy simultaneously to both antenna systems 6 and 8.

In Figure 2, of course, it is assumed that the highest audio or modulating voltage is of the order of 5000 cycles. In the event that the highest modulating frequency were higher, say, 15,000 cycles, then, of course, the frequency of the pulse oscillator POB should be increased so as to be considerably higher than the highest modulating frequency and in the case assumed might be of the order of 50,000 cycles.

A modification of our invention is illustrated in Figure 2C wherein the antenna systems 6, 8 are fed continuously with two dierent radio frequency waves derived from transmitter I and transmitter 2. These transmitters are modulated simultaneously with amplified waves derived from microphone M, audio frequency amplifier AF2 and transformer T2. The type of modulation on the waves radiated from antennas 6 and 8 may be, therefore, amplitude, phase, frequency or pulse modulation. At the receiving end, two receivers would preferably be used, tuned, respectively, to these different radio frequencies and the receivers would be so connected as to feed, in parallel, a common audio amplifier. The system of Figure 2 would also be free of dead spots or shadows cast by obstacles since the received waves would come in on one wave length or another over the entire 360 degree range. The receiving system for the transmitter of Figure 2C would be arranged as illustrated in Figure 1A with the exception that the two receivers IR and 2R would be tuned respectively to the frequencies transmitted by the antennas 6 and 8 of Figure 2C.

The transmitting system of Figure 2B combines the features of Figures 2 and 2C. Transmissions from Figure 2B may be received on the receiving system of Figure 1A.

Thus, referring to Figure 2B the pulse modulating arrangement is the same as that illustrated in Figure 2 wherein the power amplifiers PAI and PA2 are switched or alternately excited under control of the pulse oscillator P06. However, in Figure 2B each power amplifier is fed with a different radio frequency carrier derived from master oscillators MOI and M02 so that the radiations from antennas 6, 8 are alternate and at different frequencies.

As already explained, when signaling with very short waves shadows or dead spots are caused by obstacles in the path of the transmitted waves. Similar dead spots are produced when short wave signals are transmitted from a considerable altitude as, for instance, from the mast of a ship. For example, consider two antennas of different vheights HI and H2 located on a tall mast of a ship. The voltage picked up from these two antennas at varying distances from the mast is roughly indicated in Figure 3 where the solid line would indicate the variations in signal strength from the antenna at a height H2 and the dotted line would indicate the variations in signal Y strength for the antenna at the height HI. The zones of low intensity illustrated in Figure 3 are produced by destructive interference between the direct ray and the ray reflected from the earths surface which, in the case assumed, would be these zones of weak signal strength is illustrated in Figure 4. The two antennas IIC and I2C are arranged at diiferent heights so as to have displaced zones of low intensity as illustrated in Figure 3. That is to say, for example,antenna I IC may be adjusted at such a height as to have the characteristic illustrated by curve HI of Figure 3 and antenna I2C may be adjusted to such a height as to have a characteristic illustrated by curve H2 ofFigure 3 so that at all times, within the range of the system, a substantial signal is received from either or both of the transmitting antennas. The antennas are preferably omnidirectional and if placed on board ship may be of the type described in Figure 7 of the patent application of J. B. Atwood referred to hereinabove. The antennas IIC and I2C may, if desired, be

directional over something more than 180 degrees and in this case they preferably are of the type described by J. B. Atwood in his copending application referred to and in particular in Figures 3 and 4 thereof. In this event, the antennas IIC and I2C of Figure 4 may be aimed in the same direction or vin opposite directions. The antennas, as just described, may be used at the vreceiving station of Figure 1A, in which event the antennas 6A and 8A of Figure 1A would be supported at different heights and in accordance with the principles outlined in connection with Figure 3 herein.

Referring again to Figure 4, it will be noted that the transmitter arrangement is similar to that described in Figure 2. Transmitters or power ampliers MC and I5C radiate alternate pulses generated by the pulse generators under control of the pulse modulators I 6C and I'IC. The carrier frequency of the radiated pulses is that of the master oscillator MOI when switch SI is closed and switch S2 is open. When transmitting at diierent frequencies, switch SI is left open and switch S2 is closed, in which event the frequency of radiation from antenna I IC is that of the master oscillator MOI and the frequency of radiation from antenna I2C is different, then being, when switch S2 is closed, the frequency of operation of master oscillator M02. The timing of the radiated pulses from antennas I IC and I2C is controlled by a wave of super-sonic frequency generated by oscillator ISC which is cou- 4pled differentially to the pulse modulators I6C and IIC through transformer I8C. The pulse modulators IBC and I'IC are excited cophasally with modulation waves derived from microphone 20C and transformer 22C so that the pulse outputs of modulator I6C and I'IC which at the frequency of the pulse oscillator I9C would vary in length or duration, as before explained in connection with Figures 2 and 2A, in accordance with the signal at 20C.

Figure 5 shows a system whereby pulses are radiated alternately from antennas at two different heights and also in two diierent directionsy to 1 avoid theinterference of, a. local obstaclefsuclras :the: supporting tower l of. Figure 1. Inathe system. of .Figure antennas 3U .and.,3|, supported at different heights I-Il and H2, radiate in the same'general direction. Antennas v,39:,and 4D are .also supported at different heights I-II and H2 andare arranged to radiate: in the :opposite direction. If desired, antennas`39 and 40`may be arranged at heights respectively H3 and I-I4 whicharediiferent vthan the heights yHl and H2. The horizontal directivityi of all of theantennas -.3|J, SL39 and 40 may be made Vapproximately |80 degrees Wide if eifectiveradiation is desired in all directions. In this event, each antenna may be made in the form illustrated in Figures 3 and V4 of the J. B. Atwood application-hereinabove referred to.

.Transmitters or radiov frequency power` amplifiers 32 and .33 Lradiate. pulses aalternately, ,the

timing being. controlled by Waves of super-sonic frequency generated by oscillator 31 and fed through transformer 36 tothe fpulse modulators 34 and 35. The pulse modulators 34 and 35, as before explained, produce pulses of varying length, but of a frequency controlled by pulse generator 31.

Transmitters or power amplifiers 45 and'46 also radiate pulses alternately over the other antennas 39, 4B, thetiming being controlledfby the .same super-sonic oscillator 31'which, however,

feeds the pulse modulators 41 and 48 through a phase adjusting network. 38 and transformer 49. The phase adjuster38 may be constructed. in any .known Way and is adjustedso as to produce a phase change suchthat the pulses radiated by `power amplifiers 45 and 46 will occur midway between thejpulses radiated by transmitters or power amplifiers 32 and 33.

As in connection withFigures 2 and 4, all of the pulses are modulated cophasally or :simultaneously by waves picked up on microphone 50 and fed to all of the pulse modulators'34, A35, 41

fand. 48 through the vsecondary of transformer 52.

The radiorequency carrier wave is suppliedby a master oscillator :'MO5-which,-when switch -S3 is closed and-S4 is open,supplies- Wavesof the same frequency to each of ,the radio-frequency transmitters, power amplifiers orrmodulators- 32,

.33, 45 and 46. 4Whenthis is done, a simplereceiver will receive signal energy/at any distance andat any direction or height aboveground within the range of thetransmitters, 33,45 andfr46.

If desired, .switchS3 may be openedand-r switch .S4-closed, in which event theradiationfrom .an-

tennas Bil and4 3l will. .be ata frequency controlled by the master oscillator'MO 'and the radiation 'from antennas'39 and "fliwill vbe at a dierent 'frequency corresponding to that derived from master oscillator MOEA. Or, if desired, asep- `arate master oscillator,V each operating ata dif- -ferent frequency, may be connected 'so as to supply the transmitters 32,33, i5 and i6-so that the -radiations from antennas 30, 3h39 and-v4!! will be of 'different frequencies. 'Where radiation-occurs at differentfrequencies several receivers feeding into .a common modulation or signaloutput cir- `cuit should beprovided eachreceiverlhaving its radio frequency circuits tuned 1 to .aA different vone of the radiated frequencies.

As a further alternative, master oscillator -MO5 may-be used to control'the-radiation frequency of antenna 3l and antenna 3S and master oscillator MO5A may be used to supply radio frequency waves of l a 'diiferent frequency: tofanten- '.fHavng. ,thusl described 1 our invention, what i we claimiis:

,1. The method of signaling whichfincludes generating a pluralityY of carriers yof different frequency, :pulsei modulating the carriers with the Vsame signal and alternatelyradiating from difzferent, closely adjacent points, the carriers in oppositedirections over an angle greater than 180 degrees at a frequencyl corresponding to the pulse frequency. n

1,2. 1In combination, Va pair of oppositely directed directiveantennas each adapted to radiate vover .a horizontal angle greater Vthan degrees, a

source of pulse modulated waves, and instrumentalities for alternately feeding the pulse modulated-Wavesto said antennas separately at a-rate -equal to the pulsefrequency.

3. The method which includes generating a carrier Wave energy, generating pulses of constant frequency, modulating the length of the pulses, modulating the carrier Wave with the modulated pulses, and alternately radiating the `modulated carrier from' physically and electrically separated points at an alternation rate equal to the pulse frequency.

-4. In combination, a pulse oscillator, apparatus for modulating thelength of pulses derived from said oscillator, apparatus for generating carrier Waves, circuits for modulating said carrier waves 'with said modulated pulses, a pair of output circuits, and switching circuits under control of the pulse oscillatorffor alternately exciting said output circuits with said-modulated carrier waves at an alternation rate` equal to the frequency of the pulse oscillator.

-output circuits with said modulated carrier waves.

6. In combination, a pair'of antennas, an amplier individual to and supplying Waves to said antennas, a source of carrier waves connected to 'said amplifiers, a pulse oscillator, a source -of signals, 'a pair of pulse modulators supplied with Waves from` said source of signals for modulating said pulsesone of said'pulse -modulators being connected to one of Asaid ampliners and the other to the other of said amplifiers, and switching circuits under` control of waves from said source of pulse oscillations for alternately controlling'the outputs of said ampliers at pulse frequency which is given a value higher than the highest modulatingffrequency.

7. The methodof overcoming` shadows caused byolostacles when communicating on ultra short .waves of the order of ten centimeters in length which includes generatinga plurality of carrier waves of diierent frequency, pulse modulating .the carriers with the same signal and alternately radiating the carriers from different, closely adjacent points, in opposite directions over an angle greater than 180 degrees at afrequency corresponding: to the pulse frequency.

8. In a radio frequency'system, the steps of .alternately producing radio frequency carrier sig- :nals :of two. differentY frequencies in vthe l form of A=75.

consecutivezpulses .of .given time duration, `.and

9 modulating said carrier pulses in accordance Number with a modulating signal. 2,095,774 HAROLD O. PETERSON. 2,159,647 BERTRAM TREVO-R. 2,189,317 2,189,549 REFERENCES CITED 2,213,859

The following references are of record in the file of thls patent. 2,290,692 UNITED STATES PATENTS 2,297,228 Number Name Date 2,320,521 1,821,383 Goldsmith Sept. 1, 1931 2,328,944 1,853,021 Alexanderson Apr. 12, 1932 1,863,518 Young June 14, 1932 1,973,296 schroter sept. 11, 1934 15 Number 2,033,271 Aiken Mar. 1o, 1936 540,233 2,080,081 Loth et al May 11, 1937 Name Date Taylor Oct. 12, 1937 Alford May 23, 1939 Koch Feb. 6, 1940 Hershberger Feb. 6, 1940 Hahnemann Sept. 3, 1940 Roosenstein Dec. 31, 1940 Deloraine et a1 Nov. 18, 1941 Lindenblad July 21, 1942 Kramar Sept. 29, 1942 Kear June 1, 1943 Beatty Sept. '7, 1943 FOREIGN PATENTS Country Date Great Britain Oct. 9, 1941 

